Restricting user rights while he is using RDC to the DC

Hi..
I have AD envoirnment and my DC is also a File server.
We run a customised accounting package and the software provider has asked me to allow an accounts dept user to have a remote desktop connection to access the DC to run a small file to update and reindex the accounts database.

Now iam not sure how to restrict this user to just have access to one file while doing a remote dekstop connection and not fool around the DC.